Process for polymerizing propylene using a silica-supported catalyst

Abstract

A new catalyst useful in the polymerization of at least one olefin is disclosed. The catalyst comprises the product obtained by contacting silica, in random order, with (1) at least one hydrocarbon soluble magnesium-containing compound; and (2) a first modifying compound selected from the group consisting of silicon halides, boron halides, aluminum halides and mixtures thereof followed by a second modifying compound selected from the group consisting of halides having the structural formula SiH r X 2 s , where X 2 is halogen; r is an integer of 1 to 3; and s is an integer of 1 to 3 with the proviso that the sum of r and s is 4, a hydrogen halide and mixtures thereof. The product of this step is contacted with a first titanium-containing compound having the structural formula Ti(OR) m X n , where R is hydrocarbyl or cresyl; X is halogen; m is an integer of 1 to 4; and n is 0 or an integer of 1 to 3, with the proviso that the sum of m and n is 4. Finally, the product of this latter step is, in turn, contacted with a second titanium-containing compound, different from the first titanium-containing compound, having the structural formula TiX 1 p (OR 1 ) q , where X 1 is halogen; R 1 is hydrocarbyl; p is an integer of 1 to 4; and q is 0 or an integer of 1 to 3, with the proviso that the sum of p and q is 4. A catalyst system comprising the above catalyst, an aluminum-containing first cocatalyst and at least one silane second cocatalyst is also set forth. Finally, a process for polymerizing at least one olefin utilizing the catalyst system of this disclosure is taught.

What is claimed is: 
     
       1. A process for polymerizing propylene comprising polymerizing propylene under propylene polymerization conditions in the presence of a catalyst system comprising (I) a catalyst component comprising the product prepared by the steps of: (a) contacting silica, pretreated to replace surface hydroxyl groups with a surface characterized by the structural formula ##STR2##  said silica characterized by a surface area of between about 80 m 2  /g. and about 300 m 2  /g, a median particle size of between about 20 microns and about 200 microns and a pore volume of between about 0.6 cc/g. and about 3.0 cc/g., with 2-methylpentyloxymagnesium chloride;   (b) contacting the product of step (a) with silicon tetrachloride;   (c) contacting the product of step (b) with trichlorosilane, with the proviso that the concentration of said silicon tetrachloride and said trichlorosilane contacting said products of steps (a) and (b), respectively, is such that the molar ratio of said silicon tetrachloride to said trichlorosilane is in the range of between about 70:30 and about 92:8;   (d) contacting the product of step (c) with titanium tetracresylate; and   (e) contacting the product of step (d) with titanium tetrachloride;     (II) a compound selected from the group consisting of triethylaluminum and tri-n-propylaluminum; and   (III) isobutylisopropyldimethyoxysilane.   
     
     
       2. A process in accordance with claim 1 wherein said component (II) is triethylaluminum. 
     
     
       3. A process in accordance with claim 1 wherein said step (a) occurs at a temperature in the range of between about 50° C. and about 110° C. for a period of between about 1 1/2 hours and about 2 1/2 hours. 
     
     
       4. A process in accordance with claim 1 wherein said silica is pretreated by: (a) calcining said silica at a temperature of at least about 150° C. in an inert atmosphere,   (b) treating said silica with a hexaalkyl disilazane or   (c) in random order, calcining said silica at a temperature of at least about 100° C. in an inert atmosphere and treating said silica with a hexaalkyl disilazane.   
     
     
       5. A process in accordance with claim 4 wherein said calcining step (a) occurs at a temperature in the range of between about 550° C. and about 650° C. in a nitrogen atmosphere, and said hexaalkyl disilazane of steps (b) and (c) is hexamethyl disilazane.